Which of these machines laser is the best for tattoo removal; Qx-max or spectra laser?

Mat - you would be wise to find a medical clinic with a Revlite SI Q-switched YAG laser. Conbio/Candela have been manufacturing these lasers for almost 22 years and they have proven to be the safest and most reliable, especially with black ink. If your removal "stalls" after a few treatments you may want to change to the new  PicoSure but there is probably little benefit in paying the extra on a black tattoo from the outset.

The QX-Max laser is a great tattoo laser with 1064nm,  532nm Green, 650nm Red and 585nm yellow light.  It is extremely versatile for multiple tattoo inks and is the most powerful tattoo removal laser on the market.   The Lutronic Spectra laser is also a good laser.  Depending on your tattoo, both lasers could work well.